Understanding the mechanism that promotes invasion and spread of head and neck cancer (SCCHN) will provide novel mechanism-based strategies to treat this disease. Patients with SCCHN often develop resistance to treatment, which leads to tumor recurrence. Consequently, almost half of SCCHN patients die within five years of diagnosis. Despite this dismal outlook, there have been no novel treatments in over forty years, underscoring the need for new treatment strategies. Understanding the molecular mechanisms regulating head and neck cancers is essential for effective treatment. Tumor-initiating or stem cells, and invasive cells repopulate the tumor and spread to distant sites after successful treatment. Since cellular plasticity required for invasion, recurrence and spread is primarily regulated epigenetically, treatment strategies that target the epigenetic mechanism are important. The proposed study focuses on a major epigenetic regulatory mechanism that integrates invasion, and stemness-mediated treatment resistance via epithelial-to- mesenchymal transition (EMT). The central hypothesis is that EZH2 promotes SCCHN progression and recurrence by inducing rap1/EMT-mediated invasion and stemness; this critical role makes EZH2 an excellent treatment target. We will test our hypothesis by pursuing the following aims: #1) To investigate the mechanism by which EZH2 promotes invasion in SCCHN; #2) To define the mechanism of EZH2-induced treatment resistance; and #3) To evaluate the clinical relevance of EZH2 expression in human tissue. We will accomplish the objectives of this application using cell lines, 2D and novel 3D in vitro models, newly developed in vivo models of human SCCHN, and human tissue. The proposed studies will identify novel mechanisms through which rap1 integrates epigenetic reprogramming and EMT-mediated invasion, stemness and treatment resistance in SCCHN. Thus, our findings will facilitate the design of rational strategies to treat SCCHN.